PROJECT SUMMARY The objective of this NIDA K08 career development proposal is to gain experience and training to become an independent investigator focused on the development of evidence-based practices to prevent and treat substance use disorders in the emergency department. Opioid use disorders, including overdose and addiction, have become epidemic in the United States. While research has largely focused on long-term opioid prescribing in the outpatient setting, emergency department opioid prescribing for acute painful conditions as a portal for future adverse patient outcomes remains poorly defined. State governments, including the Commonwealth of Massachusetts, have reacted to the opioid crisis in part by crafting legislation to broadly limit legal opioid prescriptions. However, opioid medications remain an important treatment option for some acute painful conditions, and evidence based guidance on appropriate prescribing is lacking, in part because the factors that impact providers opioid prescribing behaviors and subsequent patient associated adverse outcomes remains unknown. Understanding the underlying factors that influence opioid prescribing behaviors and future patient outcomes, including state legislation, peer behaviors, hospital attitudes, and local culture, is a critical step in developing integrated, evidence-based recommendations that focus on transforming the culture surrounding safe opioid prescribing practices. Using the theory of planned behavior as a framework, the goals of this K08 grant application are to understand opioid prescribing behaviors and adverse patient outcomes through the following aims: First, we will assess the influence of state legislation, specifically the 2016 Massachusetts (MA) Opioid Law, on the formation of hospital-based regulations and providers' perceived attitudes towards opioid prescribing through qualitative interviews with local physician leaders in MA. Second, using comprehensive claims data, we will evaluate the impact of the 2016 MA Opioid Law on statewide opioid prescribing, using a neighboring state without opioid legislation as a natural control. Finally, we will examine the association of an initial opioid prescription on clinically relevant patient outcomes in order to better understand how restricting opioid prescriptions through legislation may impact emergency department patients presenting with an acute painful condition. From our results, we will create evidence-based recommendations to enhance existing opioid legislation, as well as develop and execute R01 funded comprehensive implementation trials that focus not only on changing behaviors of individual providers, but also transforming the group culture and social norms that influence opioid prescribing behaviors. !